tag

#int21h

3 posts

FreeDOSDeep Dive October 3, 2026 8 min read

DOS INT 21h AH=68h: Commit File Buffers Without Closing the Handle

Use DOS function 68h to request a file-handle commit, check carry and AX errors, and understand why it is not a power-loss guarantee.

#freedos#dos-api#int21h

FreeDOSDeep Dive October 3, 2026 7 min read

Read the INT 21h AH=36h register contract correctly, calculate free bytes without overflow, and handle invalid drives and changing volumes.

#freedos#dos-api#int21h

FreeDOSDeep Dive October 3, 2026 7 min read

Use DOS INT 21h AH=42h safely by handling signed CX:DX offsets, carry-flag errors, past-EOF writes, and version-dependent large-file boundaries.

#freedos#dos#int21h